1. Field of the Invention
This invention relates to the recovery of ethylene gylcol and dimethylterephthalate from scrap polyethylene terephthalate polyesters. More particularly, it relates to a simplified method of obtaining the constituent monomers of polyethylene terephthalate from scrap wherein the process is practiced under atmospheric conditions without deterioration of the yields.
2. Description of Related Art
Various methods have been disclosed heretofore for the recovery of ethylene glycol and terephthalic acid or derivatives thereof.
U.S. Pat. No 3,776,945 teaches a process of depolymerizing polyethylene terephthalate waste to obtain dimethylterephthalate and ethylene glycol by subdividing the waste into dimensions between 4 and 35 mesh and treating at a temperature of 100.degree. C. to 300.degree. C. and a pressure from 1 to 150 atmospheres with methanol in a quantity that the proportion of methanol to waste is between 1:1 and 10:1 by weight in the presence of acid catalysts.
U.S. Pat. No. 3,321,510 relates to a process of decomposing polyethyleneterephthalate by first treating with steam at a temperature of from about 200.degree. C. to 450.degree. C. and then reducing the steam-treated polyethyleneterephthalate in the form of a brittle solid product to a powder having a mean particles size of from about 0.0005 to 0.002 millimeters and subsequently atomizing the fine powder with a gaseous substance including inert gas and methanol vapor to form an aerosol which is conducted through a reaction zone at a temperature of 250.degree. C. to 300.degree. C. in the presence of excess methanol vapors.
U.S. Pat. No. 3,037,050 relates to the recovery of terephthalate acid dimethyl ester by treating polyethyleneterephthalate in the form of bulky or lumpy solid masses with super-heated methanol vapor in the presence of any suitable esterification catalyst substantially at atmospheric pressure.
U.S. Pat. No. 4,578,502 relates to a procedure for recovering monomeric polycarboxylic acids and polyols from solid scrap polyesters by granulating the scrap resin, slurring the resin with sufficient solvents such as water or methanol, depolymerizing the slurried resin by the application of heat and pressure for a time sufficient to convert substantially all of the resin into its monomeric components, crystallizing the monomeric polycarboxylic acid present by flash crystallization and recovering the polycarboxylic acid and then the polyol by distillation.
U.S Pat. No. 4,163,860 relates to a process for converting a bis-(diol) terephthalate to dimethylterephthalate by interchange in a substantially anhydrous methanol medium in the presence of a magnesium methylate catalyst.
U.S. Pat. No. 3,701,741 relates to a method of recovering substantially pure poly(ethyleneterephthalate) from scrape poly(ethyleneterephthalate) contaminated with impurities by dissolving the contaminated material at elevated temperatures and super-atmospheric pressure in a volatile solvent. This patent does not relate to the recovery of the monomeric ingredients that comprise the polymer.
U.S. Pat. No. 3,488,298 relates to a process for recovering dimethylterephthalate and ethylene glycol from poly(ethyleneterephthalate) scrap by forming a mixture comprising the poly(ethyleneterephthalate) scrape, catalyst and methanol, heating the mixture to approach equilibrium, treating the partially hydrolyzed mixture with an excess of phosphorus-containing compound, heating the treated mixture to fractionate the constituents and recovering methanol, ethylene glycol and dimethylterephthalate.
It can be seen from the above-recited art that many different techniques have been employed in the recovery of the monomeric constituents from poly(ethyleneterephthalate) resins.
These resins have found wide spread use in many and varied applications. For example, poly(ethyleneterephthalate) polyester resins find applications in the preparation of many types of films, including photographic film base, in fibers and in the preparation of food containers such as bottles and the like. Thus, there is a widespread need for a simple and economical method of treating such polyesters to recover the initial ingredients utilized in the preparation of the polyester polymers.